cmUVProcessChain: Do some internal refactoring

Move most of cmUVProcessChain::InternalData::Finish() to Prepare()
so that error codes can be checked before attepting to spawn any
processes. Check some error codes that weren't being checked before.
Change return type of Finish() to void as it can't fail.

Source/cmUVProcessChain.cxx

@@ -66,6 +66,7 @@ struct cmUVProcessChain::InternalData
 
   StreamData<std::istream> OutputStreamData;
   StreamData<std::istream> ErrorStreamData;
+  cm::uv_pipe_ptr TempErrorPipe;
 
   unsigned int ProcessesCompleted = 0;
   std::vector<std::unique_ptr<ProcessData>> Processes;
@@ -73,7 +74,7 @@ struct cmUVProcessChain::InternalData
   bool Prepare(const cmUVProcessChainBuilder* builder);
   bool AddCommand(const cmUVProcessChainBuilder::ProcessConfiguration& config,
                   bool first, bool last);
-  bool Finish();
+  void Finish();
 
   static const Status* GetStatus(const ProcessData& data);
 };
@@ -207,12 +208,23 @@ bool cmUVProcessChain::InternalData::Prepare(
         return false;
       }
 
-      errorData.BuiltinStream.init(*this->Loop, 0);
+      if (errorData.BuiltinStream.init(*this->Loop, 0) < 0) {
+        return false;
+      }
       if (uv_pipe_open(errorData.BuiltinStream, pipeFd[0]) < 0) {
         return false;
       }
       errorData.Stdio.flags = UV_INHERIT_FD;
       errorData.Stdio.data.fd = pipeFd[1];
+
+      if (this->TempErrorPipe.init(*this->Loop, 0) < 0) {
+        return false;
+      }
+      if (uv_pipe_open(this->TempErrorPipe, errorData.Stdio.data.fd) < 0) {
+        return false;
+      }
+
+      errorData.Streambuf.open(errorData.BuiltinStream);
       break;
     }
 
@@ -235,10 +247,13 @@ bool cmUVProcessChain::InternalData::Prepare(
         outputData.Stdio.flags = UV_INHERIT_FD;
         outputData.Stdio.data.fd = errorData.Stdio.data.fd;
       } else {
-        outputData.BuiltinStream.init(*this->Loop, 0);
+        if (outputData.BuiltinStream.init(*this->Loop, 0) < 0) {
+          return false;
+        }
         outputData.Stdio.flags =
           static_cast<uv_stdio_flags>(UV_CREATE_PIPE | UV_WRITABLE_PIPE);
         outputData.Stdio.data.stream = outputData.BuiltinStream;
+        outputData.Streambuf.open(outputData.BuiltinStream);
       }
       break;
 
@@ -313,31 +328,10 @@ bool cmUVProcessChain::InternalData::AddCommand(
   return process.Process.spawn(*this->Loop, options, &process) >= 0;
 }
 
-bool cmUVProcessChain::InternalData::Finish()
+void cmUVProcessChain::InternalData::Finish()
 {
-  if (this->Builder->Stdio[cmUVProcessChainBuilder::Stream_OUTPUT].Type ==
-        cmUVProcessChainBuilder::Builtin &&
-      !this->Builder->MergedBuiltinStreams) {
-    this->OutputStreamData.Streambuf.open(
-      this->OutputStreamData.BuiltinStream);
-  }
-
-  if (this->Builder->Stdio[cmUVProcessChainBuilder::Stream_ERROR].Type ==
-      cmUVProcessChainBuilder::Builtin) {
-    cm::uv_pipe_ptr tmpPipe;
-    if (tmpPipe.init(*this->Loop, 0) < 0) {
-      return false;
-    }
-    if (uv_pipe_open(tmpPipe, this->ErrorStreamData.Stdio.data.fd) < 0) {
-      return false;
-    }
-    tmpPipe.reset();
-
-    this->ErrorStreamData.Streambuf.open(this->ErrorStreamData.BuiltinStream);
-  }
-
+  this->TempErrorPipe.reset();
   this->Valid = true;
-  return true;
 }
 
 cmUVProcessChain::cmUVProcessChain()